Ruggedized computer and aspects thereof

ABSTRACT

A computer assembly having a processor integrated circuit, a hard disk drive electrically connected to the processor units and a power supply assembly, powering the processor integrated circuit and hard disk drive. These components are sealed in an liquid-tight case defining fluid channels. Electrical connectors permit connection of the processor to outside devices. Finally, a fan in the liquid-tight case, adapted to drive fluid through the fluid channel, thereby facilitates the movement of heat through the computer assembly and creates a monolithic thermal structure. In one embodiment, the computer assembly is powered by a raw DC power supply input and self manages this power input source to provide consistent and reliable power to the computer assembly without burdening the raw DC power supply during transient conditions.

RELATED APPLICATIONS

This application claims priority from provisional applications61/019,207 and 61/019,209, both filed Jan. 4, 2008 and both herebyincorporated by reference as if fully set forth herein.

TECHNICAL FIELD

The present disclosure is related to a ruggedized electrical device,able to operate reliably from a power bus that suffers intermittentvoltage reductions and aspects thereof. More specifically, theelectrical device may be a computer.

BACKGROUND

In vehicles and devices there is an increasing need for a ruggedcomputer assembly that is isolated from the elements and that canfunction with high reliability even though powered by a bus that isintermittently unable to meet the full power demand placed upon it.

SUMMARY

The embodiments described below generally address the need for aruggedized computer that can be deployed in a physical environment whereit receives physical impacts and where it may have gases, liquids andsolid/liquid mixtures (eg. mud) contacting its outside surfaces. Also,available electrical power may be subject to intermittent failure. Manyissues arise in the design of this type of device, and many of thesolutions to these issues may find application in other fields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic diagram of a mobile power system employing a powersupply unit configured in accordance with an embodiment of thedisclosure.

FIG. 2 is a schematic diagram illustrating the power supply unit of FIG.1 in more detail.

FIG. 3 is a flow diagram showing operation of the power supply unit inaccordance with an embodiment of the disclosure.

FIG. 4 is a schematic diagram of the power supply assembly in accordancewith an embodiment of the disclosure.

FIG. 5 is a side cross-sectional view of an integrated circuit and athermal assembly designed to absorb heat therefrom.

FIG. 6 is a cross-section plan view of a liquid-tight computer case andfan, according to the present invention.

DETAILED DESCRIPTION

Several aspects of the present disclosure are directed to aspects of arugged computer assembly that can function with high reliability evenwhen supplied by a bus that intermittently fails to meet power demand.Skilled persons will understand that additional embodiments may bepracticed without several of the details described below, and that otherembodiments may include aspects in addition to those described below.

FIG. 1 is a schematic diagram of a mobile power system 100 including aDC power source 102, one or more electronic devices 104, and a powersupply unit 106 that can operably couple the power source 102 with theelectronic devices 104 via input and output power busses 108 and 110. Inseveral embodiments, the power supply unit 106 can also exchange serialdata with the electronic devices 104 via a serial link 112 (describedfurther with reference to FIG. 4). In general, the power source 102provides raw DC power, and can include a variety of elements, such as abattery, an alternator, and/or any one of various types of AC-to-DCconverters. In many embodiments, the electronic devices 104 include anyof a myriad of consumer electronic devices that are configured toreceive DC power (e.g., a personal computer, a mobile phone, a GPS unit,etc.).

In other embodiments, the electronic devices 104 can be incorporatedand/or integrated with the power supply unit 106. Such a combination canbe deployed as a single unit, for example, as a computing device thatcan be energized by the (raw) DC power source on input bus 108 withoutany intervening components. In addition, embodiments of this type ofdevice can be deployed in a single rugged and protective housing, asdescribed further below with reference to FIGS. 5 and 6.

FIG. 2 is a schematic diagram illustrating the power supply unit 106 inmore detail. In the example shown in FIG. 2, the power supply unit 106includes a preregulator 210 coupled to the input bus 108. For example,in an automobile electronic system, the voltage at the input bus 108 canbe in a range of about −50 to +60V, and the preregulator 210 can stepdown this voltage to a range of about +8 to +22V. In several embodimentsthe preregulator 210 includes an automotive grade switching regulator toachieve this task. A preregulator output diode 216, couples the outputof preregulator 210 to a first internal bus 214. In turn, a main switch212 couples (and de-couples) bus 214 to output bus 110. The power supplyunit 106 also includes a battery 220 (e.g., a sealed lead acid, NiMH,LiPo battery, or UPS battery system of sufficient current capability forthe application), the positive terminal of which being connected to anoutput diode 226 terminal. The other terminal of diode 226 is connectedto a second internal power bus 224. A boost converter 228 iselectrically interposed between the first and second buses 214 and 224.For example, the boost converter 228 can output a regulated voltage in arange of about 13-14V, which can trickle charge a 12 V battery 220, or arange of 25 to 27V for charging a 24 V battery. A battery switch 222 iscouples first bus 214 to second bus 224. In a representative embodiment,the power supply unit 106 includes a logic/control assembly 230 thatcontrols the main switch 212, the battery switch 222, and the boostconverter 226. In addition, the logic/control assembly 230 can alsoexchange serial communications 232 with the electronic devices 104. Forexample, the serial communications 232 can indicate events such aswhether the battery 220 is recharging or whether the battery 220 issupplying power to the electric devices 104. Communications 232 can alsoprovide a way to change other programmable power supply 106 featuresduring operation such as program timing changes and trigger points andcan even replace the entire program for the logic control assembly 230with a newer version (described further with reference to FIG. 4).

The logic control/control assembly 230 generally operates the powersupply unit 106 in one of at least two states of operation. In a firststate of operation and/or when the preregulator output voltage V1 is ator above a predetermined trigger point, the boost converter 226 chargesbattery 220 with a boosted voltage V2 and maintains battery switch 222in an open state so that first internal bus 214 is powered bypreregulator 210, rather than battery 220. In a second state ofoperation commanded when the preregulator output voltage V1 is below thetrigger point, the logic/control assembly 230 de-activates the boostconverter 228 and couples the second bus 224 with the first bus 214 viathe battery switch 222, thereby powering devices 104 from the battery220.

FIG. 3 is a flow diagram showing an embodiment of a method of operatingthe power supply unit 106. The flow chart begins with unit 106 in thefirst operational state, its most typical condition, receivingabove-trigger point voltage on bus 108 and with boost converter 228activated and switch 222 closed. In the next instant, the logic controlassembly 230 detects whether the preregulator output voltage V1 is stillabove the trigger point (block 342), indicating an adequate voltage V1.If it is, nothing is changed (block 344). If the first bus voltage V1 isless than the predetermined trigger point, the second operational stateis commanded. Boost converter 228 is disabled and the battery switch 222is closed (block 348). In this second state, the battery 220 drives thefirst bus 214, thereby powering devices 104. From this state, V1 istested against the trigger point (block 350). The diode 216 permits ahigher voltage to exist on bus 214 than at the output of preregulator210. This is essential for sensing the restoration of preregulatoroutput voltage after a voltage low condition. (decision box 350). WhenV1 again rises above the trigger point, it is determined if timeconditions have been met (decision box 360) to switch back to the firststate (block 370), in which converter 228 is activated and 222 isclosed.

The time conditions of decision box 360 are designed to prevent a rapidtoggling between states. If, for example, V1 has been lowered due to acurrent demand from another device, the removal of the load of powersupply 106 may be enough to cause the V1 to recover in, for example, amillisecond. If there were no timing conditions, this would causeconverter 228 to be immediately reactivated, causing V1 to go low againin, for example, a millisecond. In this manner unit 106 could oscillatebetween states at a 0.5 mHz rate, which would be harmful to systemoperation. In one preferred embodiment a one second timeout isimplemented from the time converter 228 is deactivated, to the time whenit may be reactivated. Typically battery 220 stores enough charge sothat the timeout period could be made quite a bit longer than onesecond, without threatening to drain battery 220. In a preferredembodiment, timing conditions are set to match the characteristics ofthe overall system. In many embodiments the timeout function isperformed by a hysteresis circuit associated to the boost converter 226.In other preferred embodiments, the timeout function is performed by thelogic/control assembly 230.

FIG. 4 is a schematic diagram of components of the power supply unit106, including the first and second busses 214 and 224, the boostconverter 228, the switches 212 and 222, and individual logic/controlcomponents 230. More specifically, the logic control components 230include a microcontroller 360 and voltage detect components 362 and 364hardware wired to the enables of the boost converter 228 and the batteryswitch 222, respectively (in many embodiments, the boost converter 228and the battery switch 222 can also be coupled to the microcontroller360). In general, the microcontroller 360 includes a processor,associated program instructions, and system control and serialcommunication components. The voltage detect component 362 can measurewhether the first bus voltage V1 is at or above the trigger pointvoltage, and the microcontroller 360 can enable the battery switch 222and the boost converter 228 based on the detected first bus voltage V1.The voltage detect component 364, on the other hand, can measure thevoltage level of the second bus 224 and/or the battery 220. For example,the microcontroller 360 can use the voltage detect component 364 todetermine whether the battery 220 is operational and/or to determinecharge level at the battery_(—)

In many embodiments, the microcontroller 360 can also enable the mainswitch 212 depending on the state of the first and/or second busses 214and 224. If the electronic device 104 is a PC motherboard, for example,the microcontroller 360 can be configured to disable the standby orsleep voltage demand of the power supplied to the motherboard bydisabling the main switch 212 only after the motherboard hascommunicated to the microcontroller 360 that it is completely shut down.In such an example, the motherboard may have one of two interactivelogic level bits attached to the front panel header. One bit is an LEDoutput for “CPU-on” and the other is a front panel switch input bit.

The microcontroller 360 can be configured to sense the voltage at thefirst bus 214, interpret this as a “computer-on” command and activatethe motherboard. To do this, the microcontroller 360 can pulse an off/onswitch bit on the motherboard and also verify at the “CPU-on” outputthat the motherboard has booted. For example, whenever the input bus 108(or first bus 214) is powered, the microcontroller 360 can be configuredto verify that the motherboard is running or needs to be booted. Whenthe input bus 108 (or first bus 214) has been down for a predeterminedamount of time, the microcontroller 360 can interpret this is a commandto “turn off” the motherboard and do so by pulsing the on/off frontpanel bit on the motherboard and request a shutdown from a (power aware)operating system. Battery 220 provides power during an orderlymotherboard “turn off” sequence. One aspect of such a configuration ofthe microcontroller 360 is that many or all of processes carried out bythe power supply unit 106 use no (or limited) software drivers, andsystem control can accordingly be carried out exclusively in hardware,based on the state of power at the input bus 108 and the operating stateof the motherboard. This eliminates the need for a third wire, needed toindicate the beginning of a “turn off” sequence, that complicates priorart designs.

The above described system addresses numerous deficiencies in previouslyavailable power supply systems. For example, conventional power suppliesuse a boost converter-regulated front-end to maintain a tightlyregulated intermediate bus voltage during DC power deviation or “sag” atthe main bus. Such a topology demands proportionally increased currentfrom the main bus in order to offset voltage sag. This creates aconflict condition when another device on the main bus is demanding highcurrent, resulting in neither device being able to draw enough currentto maintain its required internal voltage. Also, although the typicalboost converter includes storage capacitors to provide power duringpower interrupts, these capacitors are quickly drained, again resultingin an insufficient intermediate bus voltage. Additionally, althoughexisting uninterruptible power supply (UPS) systems include a battery,the battery is typically in-line-float-charged from the boost converter.Such an arrangement causes the battery to always be in-circuit andprevents the battery from being charged at the optimum charge voltagelevel. This compromises the life of a conventional battery system andthe ability to meet current demand. Furthermore, conventional(controllable) DC based power supplies use fixed timers to control theshutdown and/or reboot sequences and times and are not interactive withexternal devices or components of an external device (e.g., amotherboard). In general, these supplies require a ‘three wire’connection with a user switch for shutdown activation, and they have nouser communication ports for real-time parameter changes or to controlsequences of operation.

Embodiments of the power supply unit 106, however, mitigate these andother issues associated with conventional power supplies and converters.For example, the boost converter 228 is disabled when the main busvoltage drops below a programmable trigger point, reducing currentdemand from the pre-regulator 210 and thereby avoiding competition withother devices for main bus current. During these periods switch 222 isclosed, permitting battery 220 to maintain proper voltage onintermediate bus 214 for far longer than do the converter storagecapacitors in existing systems. Battery 220 is either supplying power orbeing charged at an ideal charging voltage. This preserves battery lifeand maximized the probability that when the battery is called upon tosupply power it will be able to do so adequately.

Referring to FIGS. 5 and 6, the electrical network described above findsapplication in a rugged computer system. In a preferred embodiment, thissystem includes a processor integrated circuit (IC) 606 and two harddisk drives sealed within a metal case 608 (FIG. 6). One challenge inproviding a system of this type is cooling and providing thermalstability for the electrical components without a capability of blowingair in from the outside. To meet the need of cooling the processor IC606, a thermal assembly 610 is provided. This system includes the IC606, which is electrically and physically connected to a printed circuitboard (PCB) substrate 614 by a set of solder balls (not shown). A slideplate 616 is positioned above and placed in thermal contact with the IC606. In turn, a thermal mass 618 is positioned above and placed inthermal contact with the slide plate 616. Finally, the thermal mass 618is in thermal contact with the case 608. Thermal grease 619 isinterposed between and permits thermal flow between the four components606, 616, 618 and 608. Accordingly, the heat produced by IC 606 flows toslide plate 616, from whence it flows to thermal mass 618, and then tocase 608. Thermal mass 618 also acts as a heat reservoir, changing onlyslowly and preventing an overly rapid change in the temperature of IC606. The whole assembly 610 must maintain a tension to resist shock andvibration so elastomeric bumpers 612 are used to help constrain the PCBsubstrate 614 and to dampen vibration. A great challenge in the designof thermal assembly is avoiding physical damage to the system, inparticular to the solder balls connecting IC 606 to PCB substrate 614.If permitted, in the environment of physical shocks in which the ruggedcomputer is designed to be deployed, the physical mass of thermal mass618 could easily impact slide plate 616 into IC 606, thereby crushingthe solder balls or cracking IC 606. Also the heating and cooling of theproduct over its lifetime will expand and contract the internal parts atdifferent rates creating shear conditions on the connections to the IC606. To prevent damage to the solder balls, slide plate 616 is mountedfrom pins 620 mounted in PCB substrate 614 and is suspended from pins620 by tension springs 622. Accordingly, slide plate 616 can ride up anddown with IC 606 and shift in coplanar dimension relative to the contactsurfaces of IC 606, thereby avoiding stress to the solder balls and toIC 606.

Thermal mass 618 is fastened to the case 608 by stud 630. Thisconnection suspends mass 618 over slide plate 616, to control thepressure of mass 618 on slide plate 616. As noted, thermal contact ismaintained between mass 618 and slide plate 616 by thermal grease 619,which permits relative movement between the two components.

Referring specifically to FIG. 6, the above described assembly is housedin case 608 (bottom half shown), which has an internal fan 640 to blowair through a series of plenums, thereby distributing heat throughoutthe system, and stabilizing any heat contributions not alreadymechanically connected to the thermal structure. In a preferredembodiment, IC 606 produces 35 Watts of heat at full operation andassembly 610 (including case 608) takes 7 hours for its temperature tobe elevated from a starting temperature of 15° C. to 50° C. Thetemperature of assembly 610 thereafter remains at a stable 50° C. inambient air temperatures of up to 30° C. Moreover, a preferredembodiment includes a chip set that supports IC 606 and that alsorequires a thermal stack, similar to assembly 610 to remove heat andlessen thermal cycling while avoiding physical damage. In thisembodiment slide plate 616 and thermal mass 618 are made of 2024aluminum alloy, case 608 is of cast aluminum. Slide plate 616 has a massof 40.8 grams for the CPU assembly 610 and 49.9 grams for the parallelassembly for the chip set. Also, thermal mass 618 has a mass of 99.8 forthe CPU assembly 610 and 136.1 grams for the parallel assembly for thechip set. Finally, case 606 has a mass of 2536 grams and a surface areaof 1332.4 cm².

From the foregoing, it will be appreciated that representativeembodiments have been described herein for purposes of illustration, butthat various modifications may be made to these embodiments, includingadding and/or eliminating particular features. For example, in someembodiments the main switch 212 can be omitted. Also, in otherembodiments, the logic/control components 230 may include othercomponents and/or configurations. For example, one or more of thevoltage detect circuits 362 and 364 can be functionally programmed intothe microcontroller 360 (see also Appendix C). In addition, whilerepresentative examples of the system were described above in thecontext of DC power, other embodiments may include other types of power,such as DC-pulsed power or AC power. Further, while advantagesassociated with certain embodiments have been described in the contextof those embodiments, other embodiments may also exhibit suchadvantages, and not all embodiments need necessarily exhibit suchadvantages to fall within the scope of the invention. The followingexamples and appendices provide further representative embodiments.

1. A uninterruptible power supply adapted to be electrically interposedbetween a DC power bus at a first voltage level and a device that isbenefited by an uninterrupted supply of DC power at a second voltagelevel, comprising: (a) a pre-regulator connected to said DC power bus,having an output and adapted to accept electrical power at said firstvoltage level and provide power at above said second voltage level atsaid output; (b) a diode having a first terminal connected to saidoutput and oriented to prevent current flow to said output and having asecond terminal; (c) an intermediate bus connected to said diode secondterminal and also connected to said device, said second bus maintainedat approximately said second voltage; (d) a battery that is adapted tosupply power at approximately said second voltage level and adapted toaccept a charge at a third voltage level; (e) a boost converterelectrically interposed between said battery and said intermediate busand adapted to accept electric power from said intermediate bus andsupply electric power at said third voltage level to said battery input;(f) a switch coupled between said battery and said device so thatcurrent may flow from said battery to said device only when said switchis closed; (g) a diode placed so as to prevent current from flowing fromsaid battery to said pre-regulator output; and (h) a sensing and controlassembly adapted to sense a low voltage condition at said pre-regulatoroutput and to close said switch and deactivate said boost converter inresponse thereto, thereby permitting said battery to power said device,and adapted to afterwards open said switch and activate said boostconverter when a set period of time has passed and said pre-regulatoroutput voltage has been restored to a value above said second voltagelevel.
 2. The power supply of claim 1, including an additional switchbetween said intermediate bus and said device, thereby permitting saidintermediate bus to be disconnected from said device.
 3. The powersupply of claim 1, wherein said sensing and control assembly iscommunicatively connected to said device.
 4. The power supply of claim1, wherein said device is a computer.
 5. The power supply of claim 4,wherein said computer can redefine said low voltage condition.
 6. Thepower supply of claim 4, wherein a low voltage condition of greater thana predetermined duration and below a predetermined voltage level on saidDC bus is interpreted as a command to shut down said computer andresults in initiation of a shut down procedure.
 7. A uninterruptiblepower supply adapted to be electrically interposed between a DC powerbus at a first voltage level and a device that is benefited by anuninterrupted supply of DC power at a second voltage level, comprising:(a) a pre-regulator connected to said DC power bus, having an output andadapted to accept electrical power at said first voltage level andprovide power at above said second voltage level at said output; (b) adiode having a first terminal connected to said output and oriented toprevent current flow to said output and having a second terminal; (c) anintermediate bus connected to said diode second terminal and alsoconnected to said device, said second bus maintained at approximatelysaid second voltage; (d) a battery that is adapted to supply power atapproximately said second voltage level and adapted to accept a chargeat a third voltage level; (e) a boost converter electrically interposedbetween said battery and said intermediate bus and adapted to acceptelectric power from said intermediate bus and supply electric power atsaid third voltage level to said battery input; (f) a switch coupledbetween said battery and said device so that current may flow from saidbattery to said device only when said switch is closed; (g) a diodeplaced so as to prevent current from flowing from said battery to saidpre-regulator output; (h) a sensing and control assembly adapted tosense a low voltage condition at said pre-regulator output and to closesaid switch and deactivate said boost converter in response thereto,thereby permitting said battery to power said device, and adapted toafterwards open said switch and activate said boost converter when anycriteria set of a set of criteria sets is met; and (i) an additionalswitch between said intermediate bus and said device, thereby permittingsaid intermediate bus to be disconnected from said device.
 8. The powersupply of claim 7, wherein said criteria includes detection of saidpreregulator output voltage at a value above said second voltage levelafter passage of a set period of time.
 9. The power supply of claim 7,wherein said sensing and control assembly is communicatively connectedto said device.
 10. The power supply of claim 7, wherein said device isa computer.
 11. The power supply of claim 10, wherein said computer canredefine said low voltage condition.
 12. The power supply of claim 10,wherein a low voltage condition of greater than a predetermined durationand below a predetermined voltage level on said DC bus is interpreted asa command to shut down said computer and results in initiation of a shutdown procedure.
 13. A uninterruptible power supply adapted to beelectrically interposed between a DC power bus at a first voltage leveland a device that is benefited by an uninterrupted supply of DC power ata second voltage level, comprising: (a) a pre-regulator connected tosaid DC power bus, having an output and adapted to accept electricalpower at said first voltage level and provide power at above said secondvoltage level at said output; (b) a diode having a first terminalconnected to said output and oriented to prevent current flow to saidoutput and having a second terminal; (c) an intermediate bus connectedto said diode second terminal and also connected to said device, saidsecond bus maintained at approximately said second voltage; (d) abattery that is adapted to supply power at approximately said secondvoltage level and adapted to accept a charge at a third voltage level;(e) a boost converter electrically interposed between said battery andsaid intermediate bus and adapted to accept electric power from saidintermediate bus and supply electric power at said third voltage levelto said battery input; (f) a switch coupled between said battery andsaid device so that current may flow from said battery to said deviceonly when said switch is closed; (g) a diode placed so as to preventcurrent from flowing from said battery to said pre-regulator output; (h)a sensing and control assembly adapted to sense a low voltage conditionat said pre-regulator output and to close said switch and deactivatesaid boost converter in response thereto, thereby permitting saidbattery to power said device, and adapted to afterwards open said switchand activate said boost converter when any criteria set of a set ofcriteria sets is met; and (i) wherein said sensing and control assemblyis communicatively connected to said device.
 14. The power supply ofclaim 13, wherein said criteria includes detection of said preregulatoroutput voltage at a value above said second voltage level after passageof a set period of time.
 15. The power supply of claim 13, including anadditional switch between said intermediate bus and said device, therebypermitting said intermediate bus to be disconnected from said device.16. The power supply of claim 13, wherein said device is a computer. 17.The power supply of claim 16, wherein a low voltage condition of greaterthan a predetermined duration and below a predetermined voltage level onsaid DC bus is interpreted as a command to shut down said computer andresults in initiation of a shut down procedure.
 18. A uninterruptiblepower supply adapted to be electrically interposed between a DC powerbus at a first voltage level and a computer that is benefited by anuninterrupted supply of DC power at a second voltage level, comprising:(a) a pre-regulator connected to said DC power bus, having an output andadapted to accept electrical power at said first voltage level andprovide power at above said second voltage level at said output; (b) adiode having a first terminal connected to said output and oriented toprevent current flow to said output and having a second terminal; (c) anintermediate bus connected to said diode second terminal and alsoconnected to said computer, said second bus maintained at approximatelysaid second voltage; (d) a battery that is adapted to supply power atapproximately said second voltage level and adapted to accept a chargeat a third voltage level; (e) a boost converter electrically interposedbetween said battery and said intermediate bus and adapted to acceptelectric power from said intermediate bus and supply electric power atsaid third voltage level to said battery input; (f) a switch coupledbetween said battery and said computer so that current may flow fromsaid battery to said computer only when said switch is closed; (g) adiode placed so as to prevent current from flowing from said battery tosaid pre-regulator output; (h) a sensing and control assembly adapted tosense a low voltage condition at said pre-regulator output and to closesaid switch and deactivate said boost converter in response thereto,thereby permitting said battery to power said computer, and adapted toafterwards open said switch and activate said boost converter when anycriteria set of a set of criteria sets is met; and (i) wherein saidcomputer can redefine said low voltage condition.
 19. The power supplyof claim 18, wherein said criteria includes detection of saidpreregulator output voltage at a value above said second voltage levelafter passage of a set period of time.
 20. A uninterruptible powersupply adapted to be electrically interposed between a DC power bus at afirst voltage level and a computer that is benefited by an uninterruptedsupply of DC power at a second voltage level, comprising: (a) apre-regulator connected to said DC power bus, having an output andadapted to accept electrical power at said first voltage level andprovide power at above said second voltage level at said output; (b) adiode having a first terminal connected to said output and oriented toprevent current flow to said output and having a second terminal; (c) anintermediate bus connected to said diode second terminal and alsoconnected to said computer, said second bus maintained at approximatelysaid second voltage; (d) a battery that is adapted to supply power atapproximately said second voltage level and adapted to accept a chargeat a third voltage level; (e) a boost converter electrically interposedbetween said battery and said intermediate bus and adapted to acceptelectric power from said intermediate bus and supply electric power atsaid third voltage level to said battery input; (f) a switch coupledbetween said battery and said computer so that current may flow fromsaid battery to said computer only when said switch is closed; (g) adiode placed so as to prevent current from flowing from said battery tosaid pre-regulator output; and (h) a sensing and control assemblyadapted to sense a low voltage condition at said pre-regulator outputand to close said switch and deactivate said boost converter in responsethereto, thereby permitting said battery to power said computer, andadapted to afterwards open said switch and activate said boost converterwhen any criteria set of a set of criteria sets is met; and (i) whereina low voltage condition of greater than a predetermined duration andbelow a predetermined voltage level on said DC bus is interpreted as acommand to shut down said computer and results in initiation of a shutdown procedure.